I think he was torn...He DID want to be a normal guy. But he loved his father. He loved his family. He couldn't just sit back and let men come and kill his father. So, he set down on his path.

He was naive, though. He thought he could somehow worm his way out and become a Rockefeller or JP Morgan. But he couldn't. Vito was smart enough to know that you only have one path. He himself was content in his life, no regrets about being a Mafia Don. He made no apologies for how he lived his life. He wanted Michael to be legitimate, but had no problems with Sonny (had he lived and proven to be a good Don) continuing the criminal empire. He was against drugs, but only because of long term business concerns.

Michael never embraced his destiny, of being a Don, fully...And thus he wasn't as good in his role as his father was.